Typically, a liquid crystal display (LCD) panel includes an array substrate and a color filter substrate aligned with each other, as well as a liquid crystal layer sealed between the array substrate and the color filter substrate. The liquid crystal display panel includes a pixel electrode and a common electrode for forming an electric field. The electric field is generated between the pixel electrode and the common electrode by applying a voltage, so as to control alignment of liquid crystal molecules in the liquid crystal layer. Furthermore, an image can be displayed by controlling a polarization direction of incident light. Prior to application of the voltage, it is necessary to render the liquid crystal molecules to be in an initial alignment.
Available approaches for rendering the liquid crystals to be in an initial alignment include contact rubbing alignment and non-contact photo alignment. In rubbing alignment, a lint roller is used for rubbing a surface of a film to be aligned, and a physical pressure is applied, such that molecules in a surface layer of the film to be aligned are arranged in a particular direction. When the roller rubs the film to be aligned, residual dust particles, static electricity and other rubbing defects will be easily caused, which influences the product yield.
In light of the above discussion, at present, photo alignment has been gradually adopted in the industry to replace the conventional physical rubbing alignment, such that the liquid crystal molecules are regularly arranged in a fixed direction and thus have an initial alignment. In photo alignment, polarized light is obtained by allowing light (usually UV light) emitted from a light source to pass through a polarizer, and then the polarized light is used to irradiate a film to be aligned (e.g., polyimide film, PI film for short) on a substrate. In this way, the film is aligned, and optical anisotropy is introduced to the surface layer thereof. As compared with rubbing alignment, photo alignment can effectively promote the product yield and the stability of production devices.
In photo alignment, a lamp strip consisting of UV light sources and a platform for carrying a substrate to be aligned are usually configured to move at a constant speed with respect to each other, thereby initially aligning a surface of the entire substrate to be aligned. Due to influences of various factors such as manufacturing process, service life and work period, an energy magnitude of the UV light irradiating each position of the substrate to be aligned may vary. Meanwhile, the moving speed of the lamp strip also influences the energy magnitude of the UV light on the substrate to be aligned. In relevant approaches, the energy magnitude of the UV light irradiating each position of the substrate to be aligned cannot be detected locally. In this case, for the purpose of ensuring that a desired alignment effect can be achieved in all positions of the substrate to be aligned, one can only improve overall the light intensity of the UV light source on the substrate to be aligned. However, this will greatly increase the energy consumption of the UV light source and result in a rising cost. Meanwhile, for a position of the substrate to be aligned where the alignment effect can be achieved in the first place, overexposure will occur in this position due to the general increase in the energy consumption of the UV light source. Overexposure may cause damage to the performance of thin-film transistors (TFTs) on the substrate to be aligned, thereby influencing the electronic performance of the product. Moreover, overexposure may also cause deterioration of dyes in the color filter materials of the substrate to be aligned, thereby influencing the optical performance of the product.